The objective of this study is to determine factors affecting collateral ventilation in dog and horse lungs. We propose to study the effects of the parasympathetic and sympathetic nervous system, humoral mediators of the immune response, local changes in gas tensions, and changes in the pulmonary vasculature on collateral flow resistance, time constants for collateral ventilation, and compliance of the isolated lung segment. We will use a double lumen catheter to isolate a sublobar segment of lung. Air will flow into the segment through the outer lumen of the catheter and leave the segment via collateral channels. The inner lumen will record segment pressure. Using this information we will calculate collateral flow resistance and following flow interruption, collateral time constants and segment-compliance. Studies will be performed on intact dogs before and after blocking or stimulating the autonomic nerves to the lung. Mediators and circulatory effects will be studied using an excised perfused lung.